I definitely see them as a Monster band. I feel like people who say they're mainstage worthy are overestimating their popularity. However, with a new album, (that is well received) they could easily make the jump IMO, so by the time warped rolls around, they may be a perfect fit for main.
I honestly think they're a mainstage band, and I'm not saying that because of the fact I like their music or any real bias. I went to multiple Warped Tour dates this summer, guess what band shirt everyone was wearing, The Wonder Years. Admittedly I live on the east coast so it could be different out west but Kevin Lyman has stated multiple times when judging bands for Warped he looks at what the kids are wearing to figure out what will be big come next summer. If they had played this year I imagine they probably would have been a Monster band that would have gotten the bump multiple times to the main stage.